You have an extra step when you want to transfer files to and from a computer using a USB cable in Android Marshmallow.
When you plug your Marshmallow-powered phone into a computer — Windows, Mac or Linux makes no difference — you'll have to tell the operating system what you want to do.
By default, your phone (or tablet) will be in USB charging only mode. This means no data is going back and forth between your phone and your computer's USB port, and only the 5 volt power is active. That's good for charging the battery, but means you can't see the phone in any type of file or folder browsing software, and the Android File Transfer app for Mac computers will pop out an error. Every time.
What you'll need to do is go into your notifications, and tap the USB connection entry. You'll get a dialog that allows you to change things.
- Charging only is the default, and is used when all you want to do is top off your battery.
- Transfer files (MTP) lets you copy files back and forth between your phone and computer using the Media Transfer Protocol. This is likely the option you'll want if you need to copy some files.
- Transfer files (PTP) lets you copy files (usually only photos or video) using the Picture Transfer Protocol. This modes makes your computer think you have a digital camera attached, so programs that were designed to connect to a camera can grab photos and video directly from your phone and import them automatically.
- MIDI is the option you'll use if you want to connect a MIDI device — something like a MIDI keyboard — to your phone or tablet and use a synthesizer app to create music.
These look like good options all around. The inclusion of MIDI support will make a lot of people happy, and MTP and PTP are options we've been using for a while. The issue is that you can't set any of them as the default, and you need to choose each and every time.
Choosing the correct option is not a difficult step, but in previous versions you could set a connection type as a default. This feels like a step backwards, and any of the reasons we have seen or can think of don't seem very sound. Here's hoping Google gives us a default setting option back in a future update.